MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

So I did cleaning of the area above and now machine fans turn on for one second and then turn off, like quarter fan spin.

I will replace BIOS chip

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

I replaced BIOS chip, issue remains.

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

Can anyone help?

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

Can anyone advise further?

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

Hi @mon2, can you help?

[mon2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

Hi. See attached.

Remove all power. Meter in resistance mode.

Use the lowest scale on your meter.

Confirm the resistance from the topside of R7020 current sense resistor to the current sense pin CHGR_CSI_P (pin # 28).

So you are measuring from CHGR_CSI_R_P --> pin #28 of U7000.

What is the resistance in ohms ?

Repeat for the other side of the current sense resistor R7020 and CHGR_CSI_N (pin # 27).

So you are measuring from CHGR_CSI_R_N --> pin #27 of U7000.

For each, measure right at the pin on the U7000 IC - we want to be 100% sure the traces are reaching the current sense resistor legs.

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

Hi mon2,

CHGR_CSI_R_P --> pin #28 of U7000: 00.5 on 200 mode

CHGR_CSI_R_N --> pin #27 of U7000: 00.6 on 200 mode

[mon2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

Do you have a lower meter scale on your multimeter ?

If not, short the 2 meter leads and post your measurement.

Then, again with no power, measure the resistance betwee then the pins of resistor @ R7021. What is the reading ?

Then again for R7022.

Each must be 10 ohms else something is wrong. These resistor values are critical.

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

Hi mon2,

No this is lowest scale!

00.6 by shorting, on 200 mode.

R7021: 10.6

R7022: 10.6

[mon2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

Ok. The resistor readings are good on their own.

Now check again from one side of the resistor to the actual chip pin. No power in resistance checks.

If you still read 0.6 then you are on the wrong side of the resistor.

Check the OTHER side of the 10.6 ohm resistor(s) to the IC.

What are the readings ?

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

Hi mon2,

Showing 0.6 on one side and 20 on other. See photo, this is where I measured 20:

[mon2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

See attached.

Measure from the 2 arrow heads as shown for the first check.

Reading ?

Then repeat for the 2nd resistor check.

Reading ?

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

1: 07.8
2: 08.0

[mon2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

Weird - yet you have proper readings up above across each resistor ?

R7021: 10.6
R7022: 10.6

Check again for the resistors only and then trace the side from the resistor pad to the IC pad. This should be 0 ohms for each leg. Otherwise you have a PCB trace that is faulty.

Zoom out with your microscope and share another pic with the R7021 & R7022 resistors. You have a PCB trace fault here somewhere.

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

Across each resistor now measuring 06.2 on both

[mon2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

Remove one of these resistors and check the resistance out of the circuit.

Each should be very close to 10 ohms.

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

Showing 10.3 out of circuit.

[Gigabit2]

Re: MacBook Pro Mid 2012 turns on, fans spin for five seconds and turns off, repeats

What I do not understand is now out of circuit, I measure other one still in circuit and also showing 10.3! Multimeter misread?